Downhole tools for use in oil and gas wellbores often have drillable components made from metallic or non-metallic materials, such as soft steel, cast iron, engineering grade plastics, and composite materials.
In the drilling or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well, such as when it is desired to pump cement or other slurry down the tubing and force the slurry out into a formation. It thus becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Downhole tools referred to as packers and bridge plugs are designed for these general purposes and are well known in the art of producing oil and gas.
Bridge plugs isolate the portion of the well below the bridge plug from the portion thereabove. Bridge plugs therefore may experience a high differential pressure and must be capable of withstanding the pressure so that the bridge plug seals the well and does not move in the well after it has been set.
Bridge plugs make use of metallic or non-metallic slip segments, or slips, that are initially retained in close proximity to a mandrel but are forced outwardly away from the mandrel of the tool upon the tool being set to engage a casing previously installed within an open wellbore. Upon the tool being positioned at the desired depth, or position, the slips are forced outwardly against the inside of the casing to secure the packer, or bridge plug as the case may be, so that the tool will not move relative to the casing when, for example, operations are being conducted for tests, to stimulate production of the well, or to plug all or a portion of the well.
Cylindrically shaped inserts, or buttons, may be placed in such slip segments, especially when the slip segments are made of a non-metallic material such as plastic composite material, to enhance the ability of the slip segments to engage the well casing. The buttons must be of sufficient hardness to be able to partially penetrate, or bite into, the surface of the well casing which is typically steel. However, especially in the case of downhole tools being constructed of materials that lend themselves to being easily drilled from the wellbore once a given operation involving the tool has been performed, the buttons must not be so hard or so tough to resist drilling or fouling of the cutting surfaces of the drilling bit or milling bit.
A retaining ring is disposed about the slip segments, generally in a groove in the slip segments, to hold the slip segments in an unset position prior to the slip segments being forced outwardly into the casing. The retaining ring is intended to prevent the slip segments from moving outwardly prematurely. When the slip segments move radially outwardly, the retaining ring breaks, so that the slip segments can move outwardly to engage the casing to secure the tool in the well. The retaining rings often have a “spring effect” upon breaking which causes the broken retaining band to spring with enough energy to move away from the slip segments. The retaining ring may move or spring enough to wedge between the slip segments and the casing, or other part of the tool and the casing and can prevent the tool from setting, sealing or operating properly in the well. There is a need for a retaining ring that will apply sufficient holding force, but that will have a limited spring effect.